This invention relates in general to conveyor systems and in particular to a system using continuous unbroken loops of polyurethane belting travelling in parallel paths and supporting trays or other carriers of material.
The invention has its primary application in the food service industry, but obviously may be used in shipping, warehousing or other activities where it is necessary to move articles from one point to another for assembly, disposal, or other purpose.
Conveyor systems have long been used in the food service industry for such purposes as assembling meals on individual trays or for transporting soiled trays to a point where used items may be disposed of and utensils and dishes may be washed. Commonly, these systems are set up in generally looped configurations. Quite often, the loop is in the form of an oval and work stations may be set up along one or both of the long sides of the oval for the assembly of items on a food tray or, conversely, for the placement of trays of soiled items or their removal from the conveyor belt. In order to drive these conveyor systems, it was early the practice to use endless loops of chains which flex in the manner of a bicycle drive chain. These were driven by a drive motor with a sprocket which engaged the chain at a 180.degree. turning point along the conveyor path. Trays or other carriers were attached at intervals to the chains. Because of their complexity, weight, and difficulty in maintaining sanitary measures, chain type drives were not satisfactory. Also, because it was necessary at times for the conveyor path to be curved in order, for example, to get around obstacles such as pillars, chain drives were abandoned in favor of belts or cables of flexible polymeric material. These belts at some point in their travel would be wrapped about a drive shaft from which they derived their motion.
Typical of a very early arrangement of conveyor utilizing generally parallel cables is that disclosed in U.S. Pat. No. 1,476,936. As the patentee notes, two cables are provided, and these form the moving mechanism of the conveyor and a receptacle containing the product may rest upon and be carried by the cables. Change of direction is accomplished by utilizing suitable sheaves around which the endless cables pass. At each corner that the conveyor belt turns, there are two independently rotating coaxial idler sheaves. The idler sheaves are of different diameters, but the cables are of equal length. By utilizing a constant speed and an even number of corners, containers of product may be carried along a plurality of paths from one point to another. However, because the two pulleys about which the cables pass are mounted vertically one above the other, one of the cables at the corners is higher than the other and containers carried by the cables are tilted as they turn the corner. This condition is inherently hazardous and especially not tolerable in a food-carrying operation where food will be spilled or otherwise displaced on carrier trays as corners are turned. Also, of course, the arrangement of vertically mounted sheaves is cumbersome and expensive and is not adaptable to conveyors having tortuous paths or odd numbers of corners.